1. Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into a plurality of devices, the wafer including a substrate and a functional layer formed on the substrate, the plural devices being formed from the functional layer.
2. Description of the Related Art
Conventionally known is a semiconductor wafer including a substrate such as a silicon substrate and a functional layer formed on the front side of the substrate, wherein a plurality of devices are formed from the functional layer. The functional layer is formed by stacking a plurality of low-permittivity insulator films (low-k films). Examples of each low-k film include an inorganic film of SiO2, SiOF, etc., a polymer film of polyimide, parylene, etc., and an organic film of SiOC, etc. Each low-k film is very brittle like mica. Accordingly, when the wafer having the stacked low-k films is cut by using a cutting blade, there arises a problem such that the low-k films may be separated (delamination) to cause damage to the devices. To cope with this problem, there has been proposed a wafer processing method including the steps of applying a laser beam along each street formed on the wafer to form two laser processed grooves along each street which grooves are spaced a given distance greater than the width of the cutting blade, thereby dividing the low-films, and next cutting the area between the two laser processed grooves along each street, whereby the separation of the low-k films can be stopped by the two laser processed grooves to prevent the damage to the devices (see Japanese Patent Laid-open No. 2005-142398, for example).